Tryptophan-functionalized gold nanoparticles for deep UV imaging of microbial cells

• Gold nanoparticles were functionalized with amino acid tryptophan (Trp).
• Trp layers on Au yielded photoluminescence of the nanostructures in the UV region.
• Au–Trp nanostructures were used as fluorescent probes for DUV imaging of E. coli.
• The spatial distribution of the nanoparticles within individual cells was followed.

Biocompatible fluorescent nanostructures were prepared by a functionalization of gold nanoparticles with the amino acid tryptophan. The gold-tryptophan bioconjugates were investigated by TEM and HRTEM and various spectroscopy methods (XPS, FTIR, UV–vis and photoluminescence). It was found that the gold nanoparticles, initially 8 nm in diameter, aggregate in the presence of the amino acid. From the XPS and FTIR spectroscopy results, it was concluded that the tryptophan gold interactions mainly take place via indole and carboxyl groups. Although the indole group is involved in the interaction with the gold surfaces, the tryptophan–gold hybrids showed strong fluorescence due to the presence of multilayers of tryptophan. Deep ultra violet (DUV) imaging performed at the SOLEIL synchrotron showed that it is possible to detect these hybrid nanostructures within Escherichia coli cells.

Deep UV fluorescence image of E. coli cells incubated with tryptophan-functionalized gold nanoparticles.Figure optionsDownload as PowerPoint slide